In recent years, a wearable terminal that is capable of continuously keeping a record of daily life as a life-log has been introduced. The wearable terminal is a terminal device that can be used while being worn by a user at all times. The wearable terminal has a camera and a microphone, and is capable of keeping the record at all times without an operation by the user.
A patent document 1 discloses a wearable terminal that supports the memory and memory recall of the user by defining importance levels of information pieces acquired from the camera and the microphone for each event, and capturing these information pieces according to the importance levels. However, it is problematic that, due to a usage act that the wearable terminal keeps on capturing images while being worn by the user at all times, the qualities of the captured images notably deteriorate because of a motion of the user. In particular, it is problematic that when images are captured with the wearable terminal tilting off the horizontal, the captured images are tilted.
Meanwhile, a Patent document 2 discloses a method of correcting a tilt of a captured image by detecting line segments that exist in an upper part of the captured image, and estimating a tilt angle of the captured image as a whole based on tilt angles of the line segments. In the image correction method disclosed in the Patent document 2, it is presumed that the image is captured with the user standing substantially straight. Therefore, when the image is captured with the user standing substantially straight, it is expected that it is difficult to estimate a horizontal direction based on line segments that exist in a lower part of the captured image due to an influence by a ground and a shadow, while it is easy to estimate the horizontal direction based on line segments of structural objects and the like that exist in the upper part of the captured image. The method disclosed in the Patent document 2 has a feature of correcting the captured image by actively making use of the above-stated features of the captured image.    Patent document 1: Japanese Laid-open Patent Application Publication No. 2003-304486    Patent document 2: Japanese Patent Publication No. 3676360